Metal Content of E-coat

Ask an Expert From: Products Finishing, , from Ti6 Consulting International

Posted on: 3/3/2014

Which metals could be present in a zinc phosphate pretreatment layer and a cathodic epoxy electrocoat layer?

Q. New laws have my company investigating what metal elements our finishing department incorporates into the products we manufacture after they are processed through a cathodic epoxy electrocoat line with a zinc phosphate pretreatment. Could you help me break down which metals could be present in the pretreatment layer and in the electrocoat layer?— J.M. 

A. I know there are many new and “exciting” regulatory reporting requirements imposed on electrocoaters who provide coating services in the U.S., as well as in Europe. Current legislative mandates that require some kind of metal identification and reporting include REACH, IMDS, Conflict Minerals, RoHS, etc. Some reporting requirements go as far as mandating that coaters identify and report not only the metallic content, but the source of the smelter producing the metal, the name of the company mining the ore and the country where this mining takes place.  

To give you an idea of all metallic elements present in a product that has been processed through a zinc phosphate and epoxy cathodic line, I first must assume that the zinc phosphate employed is a typical automotive, unmodified, tri-cationic zinc phosphate. Also, I have to assume that the sealer employed is a non-chrome sealer. 

The pretreatment layer could incorporate titanium (Ti) from the activator. The phosphate layer could potentially incorporate zinc (Zn), nickel (Ni) and manganese (Mn), in addition to some potential iron (Fe) from migration reactions from the substrate. Lastly, the sealer step could incorporate zirconium (Zr), as this technology is widely used as a non-chrome sealer. Summarizing, the pretreatment layer could incorporate Ti, Zn, Ni, Mn, Fe and Zr.

There are industrial pretreatment technologies available today that can potentially eliminate most metallic elements encountered in typical automotive phosphate systems. However, some of those technologies still cannot provide the level of extended and extreme performance that automotive tri-cationic phosphate systems currently achieve.

In terms of the electrocoat layer, I have to assume that it is black, and that it is late-generation and so does not include lead (Pb) or chrome (Cr). Because the pigment would be mostly due to carbon black, the only potential metal present in the electrocoat layer would be tin (Sn) or bismuth (Bi). These metals are typically used as catalysts to control the polymerization of the electrocoat during cure. Future electrocoat technologies will be completely metal-free as paint companies will introduce metal-free catalysts in their formulas. 

As you can see, most of the metallic elements introduced by your finishing department come from the pretreatment step and not the electrocoat step. Soon, electrocoats will be considered entirely metal-free.


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